Field of the Invention
The present invention relates to a servomotor control device and a production system equipped with the control device.
Description of the Related Art
In a production system, a robot and a positioner include motors in every drive shaft, and these motors are drive-controlled by a motor control device. For example, a servomotor is used for controlling rotation or trace of a workpiece arranged in the positioner. The motor control device instructs and controls motor speed, torque, and a position of a rotor, with respect to the motors for driving the drive shafts of the robot and the positioner, the number of which motors corresponds to the number of the drive shafts.
In the production system, a worker sometimes performs various operations, such as attaching/detaching of a workpiece to/from the positioner and performing of a confirming operation for confirming the operation state of the robot, in a movable range of the robot. When the worker works in the movable range of the robot, there is a common area that is an area in which a working range of the worker and the movable range of the robot are overlapped. In order to prevent accidental contact between the worker and the robot from occurring, a light curtain for detecting the entry of a worker into the common area is sometimes arranged. When the light curtain detects the entry of a worker into the common area, a robot having a movable range in the common area, and a servomotor for driving the robot are emergency-stopped. In a conventional production system, when emergency-stopping a servomotor, the servomotor is stopped by disconnecting a connection between a power source and the servomotor by an electromagnetic contactor arranged between the power source for supplying a power-supply voltage to the servomotor and a servo amplifier for controlling the servomotor.
However, there are various problems caused by emergency-stopping the servomotor by operating the electromagnetic contactor arranged between the servo amplifier and the power source every time the worker enters the common area. For example, by disconnecting the connection between the power source and the servo amplifier in the emergency stop, a capacitor arranged in the servo amplifier is discharged, and thus, the capacitor arranged in the servo amplifier is charged in restarting the servomotor. Since the capacitor of the servo amplifier is charged at every emergency stop, it takes time to emergency-stop and restart the servomotor, and the working efficiency of the production system may be decreased.
In addition, when the servomotor is emergency-stopped by performing an opening operation of the electromagnetic contactor every time the worker enters the common area, the number of opening/closing operations of the electromagnetic contactor may be considerably increased. When the servomotor is emergency-stopped by performing an opening operation of the electromagnetic contactor every time a workpiece arranged in a positioner of a robot is replaced, the replacement cycles for replacing the electromagnetic contactor, a relay circuit for operating the electromagnetic contactor and the like may be shortened.
In addition, the electromagnetic contactor is sometimes arranged between a plurality of servo amplifiers each of which controls a plurality of servomotors and a power source. When the electromagnetic contactor is arranged between the plurality of servo amplifiers and the power source, emergency-stopping a servomotor of a robot having a movable range in the common area may concurrently emergency-stop a servomotor of a robot not having a movable range in the common area. By emergency-stopping the servomotor of the robot not having a movable range in the common area, the working efficiency of the production system may be further decreased.